1,413 research outputs found
Extended polarized semiclassical model for quantum-dot cavity QED and its application to single-photon sources
We present a simple extension of the semi-classical model for a two-level
system in a cavity, in order to incorporate multiple polarized transitions,
such as those appearing in neutral and charged quantum dots (QDs), and two
nondegenerate linearly polarized cavity modes. We verify the model by exact
quantum master equation calculations, and experimentally using a neutral QD in
a polarization non-degenerate micro-cavity, in both cases we observe excellent
agreement. Finally, the usefulness of this approach is demonstrated by
optimizing a single-photon source based on polarization postselection, where we
find an increase in the brightness for optimal polarization conditions as
predicted by the model.Comment: 8 pages, for simple code see https://doi.org/10.5281/zenodo.347666
Search for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri e
[Abridged] The aim of this work is to search for an absorption signal from
exospheric sodium (Na) and singly ionized calcium (Ca) in the optical
transmission spectrum of the hot rocky super-Earth 55 Cancri e. Although the
current best-fitting models to the planet mass and radius require a possible
atmospheric component, uncertainties in the radius exist, making it possible
that 55 Cancri e could be a hot rocky planet without an atmosphere. High
resolution (R110000) time-series spectra of five transits of 55 Cancri e,
obtained with three different telescopes (UVES/VLT, HARPS/ESO 3.6m &
HARPS-N/TNG) were analysed. Targeting the sodium D lines and the calcium H and
K lines, the potential planet exospheric signal was filtered out from the much
stronger stellar and telluric signals, making use of the change of the radial
component of the orbital velocity of the planet over the transit from -57 to
+57 km/sec. Combining all five transit data sets, we detect a signal
potentially associated with sodium in the planet exosphere at a statistical
significance level of 3. Combining the four HARPS transits that cover
the calcium H and K lines, we also find a potential signal from ionized calcium
(4.1 ). Interestingly, this latter signal originates from just one of
the transit measurements - with a 4.9 detection at this epoch.
Unfortunately, due to the low significance of the measured sodium signal and
the potentially variable Ca signal, we estimate the p-values of these
signals to be too high (corresponding to <4) to claim unambiguous
exospheric detections. By comparing the observed signals with artificial
signals injected early in the analysis, the absorption by Na and Ca are
estimated to be at a level of approximately 2.3 and 7.0 respectively, relative to the stellar spectrum.Comment: 15 pages, 8 figures, submission updated after English language
editing, submission updated to correct a mistaken cross-reference noticed in
A&A proo
Optical to near-infrared transit observations of super-Earth GJ1214b: water-world or mini-Neptune?
GJ1214b is thought to be either a mini-Neptune with a thick, hydrogen-rich
atmosphere, or a planet with a composition dominated by water. In the case of a
hydrogen-rich atmosphere, molecular absorption and scattering processes may
result in detectable radius variations as a function of wavelength. The aim of
this paper is to measure these variations. We have obtained observations of the
transit of GJ1214b in the r- and I-band with the INT, in the g, r, i and z
bands with the 2.2 meter MPI/ESO telescope, in the Ks-band with the NOT, and in
the Kc-band with the WHT. By comparing the transit depth between the the
different bands, which is a measure for the planet-to-star size ratio, the
atmosphere is investigated. We do not detect clearly significant variations in
the planet-to-star size ratio as function of wavelength. Although the ratio at
the shortest measured wavelength, in g-band, is 2sigma larger than in the other
bands. The uncertainties in the Ks and Kc bands are large, due to systematic
features in the light curves. The tentative increase in the planet-to-star size
ratio at the shortest wavelength could be a sign of an increase in the
effective planet-size due to Rayleigh scattering, which would require GJ1214b
to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have
both clouds, to suppress planet-size variations at red optical wavelengths, as
well as a sub-solar metallicity, to suppress strong molecular features in the
near- and mid-infrared. However, star spots, which are known to be present on
the hoststar's surface, can (partly) cancel out the expected variations in
planet-to-star size ratio, due to the lower surface temperature of the spots .
A hypothetical spot-fraction of 10% would be able to raise the infrared points
sufficiently with respect to the optical measurements to be inconsistent with a
water-dominated atmosphere. [abridged]Comment: 13 pages, 8 figures. Accepted for publication in A&
Never injected, but hepatitis C virus-infected: a study among self-declared never-injecting drug users from the Amsterdam Cohort Studies
The aim of this study was to gain insight in transmission routes of hepatitis C virus (HCV) infection among never-injecting drug users (DU) by studying, incidence, prevalence, determinants and molecular epidemiology of HCV infection. From the Amsterdam Cohort Studies among DU, 352 never-injecting DU were longitudinally tested for HCV antibodies. Logistic regression was used to identify factors associated with antibody prevalence. Part of HCV NS5B was sequenced to determine HCV genotype and for phylogenetic analyses, in which sequences were compared with those from injecting DU. HCV antibody prevalence was 6.3% and HCV incidence was 0.49/1000 PY. HIV-positive status, female sex and starting injection drug use during follow-up (a putative marker of past injection drug use), were independently associated with HCV prevalence. The main genotypes found were genotype 3a (50%) and 1a (30%). Phylogenetic analysis revealed that HCV strains in never-injecting DU did not cluster together and did not differ from HCV strains circulating in injecting DU. We found a higher HCV prevalence in never-injecting DU than in the general population. Phylogenetic analysis shows a strong link with the injecting DU population. The increased risk could be related to underreporting of injecting drug use or to household or sexual transmission from injectors to noninjectors. Our findings stress the need for HCV testing of DU who report never injecting, especially given the potential to treat HCV infection effectively
Stimulated emission of polarization-entangled photons
Entangled photon pairs -- discrete light quanta that exhibit non-classical
correlations -- play a crucial role in quantum information science (for example
in demonstrations of quantum non-locality and quantum cryptography). At the
macroscopic optical field level non-classical correlations can also be
important, as in the case of squeezed light, entangled light beams and
teleportation of continuous quantum variables. Here we use stimulated
parametric down-conversion to study entangled states of light that bridge the
gap between discrete and macroscopic optical quantum correlations. We
demonstrate experimentally the onset of laser-like action for entangled
photons. This entanglement structure holds great promise in quantum information
science where there is a strong demand for entangled states of increasing
complexity.Comment: 5 pages, 4 figures, RevTeX
A complementarity-based approach to phase in finite-dimensional quantum systems
We develop a comprehensive theory of phase for finite-dimensional quantum
systems. The only physical requirement we impose is that phase is complementary
to amplitude. To implement this complementarity we use the notion of mutually
unbiased bases, which exist for dimensions that are powers of a prime. For a
d-dimensional system (qudit) we explicitly construct d+1 classes of maximally
commuting operators, each one consisting of d-1 operators. One of this class
consists of diagonal operators that represent amplitudes (or inversions). By
the finite Fourier transform, it is mapped onto ladder operators that can be
appropriately interpreted as phase variables. We discuss the examples of qubits
and qutrits, and show how these results generalize previous approaches.Comment: 6 pages, no figure
De Broglie Wavelength of a Nonlocal Four-Photon
Superposition is one of the most distinct features of quantum theory and has
been demonstrated in numerous realizations of Young's classical double-slit
interference experiment and its analogues. However, quantum entanglement - a
significant coherent superposition in multiparticle systems - yields phenomena
that are much richer and more interesting than anything that can be seen in a
one-particle system. Among them, one important type of multi-particle
experiments uses path-entangled number-states, which exhibit pure higher-order
interference and allow novel applications in metrology and imaging such as
quantum interferometry and spectroscopy with phase sensitivity at the
Heisenberg limit or quantum lithography beyond the classical diffraction limit.
Up to now, in optical implementations of such schemes lower-order interference
effects would always decrease the overall performance at higher particle
numbers. They have thus been limited to two photons. We overcome this
limitation and demonstrate a linear-optics-based four-photon interferometer.
Observation of a four-particle mode-entangled state is confirmed by
interference fringes with a periodicity of one quarter of the single-photon
wavelength. This scheme can readily be extended to arbitrary photon numbers and
thus represents an important step towards realizable applications with
entanglement-enhanced performance.Comment: 19 pages, 4 figures, submitted on November 18, 200
Long-term survival after hyperthermic intraperitoneal chemotherapy using mitomycin C or oxaliplatin in colorectal cancer patients with synchronous peritoneal metastases:A nationwide comparative study
Objectives: In the Netherlands, limited variability exists in performance of cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC) among centers treating colorectal peritoneal metastases (PM), except for the intraperitoneal drug administration. This offers a unique opportunity to investigate any disparities in survival between the two most frequently used HIPEC regimens worldwide: mitomycin C (MMC) and oxaliplatin.Methods: This was a comparative, population-based cohort study of all Dutch patients diagnosed with synchronous colorectal PM who underwent CRS-HIPEC between 2014 and 2017. They were retrieved from the Netherlands Cancer Registry. Main outcome was overall survival (OS). The effect of the intraperitoneal drug on OS was investigated using multivariable Cox regression analysis.Results: In total, 297 patients treated between 2014 and 2017 were included. Among them, 177 (59.6%) received MMC and 120 (40.4%) received oxaliplatin. Only primary tumor location was different between the two groups: more left-sided colon in the Oxaliplatin group (47.5% vs. 33.3%, respectively, p=0.048). The 1-, 2- and 3-year OS were 84.6% vs. 85.8%, 61.6% vs. 63.9% and 44.7% vs. 53.5% in patients treated with MMC and oxaliplatin, respectively. Median OS was 30.7 months in the MMC group vs. 46.6 months in the oxaliplatin group (p=0.181). In multivariable analysis, no influence of intraperitoneal drug on survival was observed (adjusted HR 0.77 [0.53-1.13]).Conclusions: Long-term survival between patients treated with either MMC or oxaliplatin during CRS-HIPEC was not significantly different. (C) 2020 Elsevier Ltd, BASO similar to The Association for Cancer Surgery, and the European Society of Surgical Oncology. All rights reserved.</p
Does the Risk of Childhood Diabetes Mellitus Require Revision of the Guideline Values for Nitrate in Drinking Water?
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